Results. Gender explained 33-42% of the variation in knee cartilage volumes (all P < 0.001). Males had 33-42% higher cartilage volume than females at all sites. In the whole group, the magnitude of sex differences decreased to 8-18% after adjustment for body height, weight and bone size, but remained significant (all P < 0.05). Further adjustment for physical activity had no effect on the sex differences. The sex differences in cartilage volume were greater in those aged over 50 compared with those aged under 50 (P < 0.05 for age-sex interaction at all sites) and were independent of ROA.

Conclusions. Men have substantially higher knee cartilage volumes than women. These sex differences appear to be mediated in part by body and bone size but a significant amount remains unexplained. Furthermore, the differences become more marked over the age of 50 yr suggesting that both cartilage development and cartilage loss in later life contribute to sex differences in cartilage volume. Further longitudinal studies in large samples will be required to confirm these findings.